New insights into the magnetism and magnetic structure of LuCrO₃ perovskite

A polycrystalline sample LuCrO₃ has been characterized by neutron powder diffraction (NPD) and magnetization measurements. Its crystal structure has been Rietveld refined from NPD data in space group Pnma; this perovskite contains strongly tilted CrO₆ octahedra with extremely bent Cr-O-Cr superexchange angles of ∼142°. The NPD data show that below Néel temperature (T_N ≃ 131 K), the magnetic structure can be defined as an A-type antiferromagnetic arrangement of Cr³⁺ magnetic moments, aligned along the b axis, with a canting along the c axis. A noticeable magnetostrictive effect is observed in the unit-cell parameters and volume upon cooling down across T_N. The AC magnetic susceptibility indicates the onset of magnetic ordering below 112.6 K; the magnetization isotherms below T_N show a nonlinear behaviour that is associated with the described canting of the Cr³⁺ magnetic moments. From the Curie-Weiss law, the effective moment of the Cr³⁺ sublattice is found to be μ_eff = 3.55 μ_B (calculated 3.7 μ_B) while the Θ_CW parameter yields a value of -155 K, indicating antiferromagnetic interactions. There is a conspicuous increase of T_N upon the application of external pressure, which must be due to shortening of the Cr-O bond length under compression that increases the orbital overlap integral.